Ba-lance slide-valve



(No Model.)

W. A. DOBSON. BALANCE SLIDE VALVE.

No. 339,979. Patented Aprf13, 1886.

2/7 5.. WITNESSES UNITED STATES "PATENT @FricE.

WILLIAM A. DOBSON, OF BLOOMINGTON, ILLINOIS.

BALANC E SLl DE- VALVE.

SPECIFICATION forming part of Letters Patent No, 339,979, dated April 13, 1886?.

Renewed December 31, 1895.

Serial No. 187,311. (No model.)

T 0 all whom it may concern:

Be it known that 1, WILLIAM A. DoBsoN, a citizen of theUnited States, residing at Bloomington, in the county of McLean and State of Illinois, have invented certain new and useful Improvements in Balance Slide-Valves, of which the following is a specification, reference being had to the accompanying drawings.

This invention relates to certain improvements in slide-valves for steam-engines.

The ordinary slide valve is objectionable, owing to the resistance caused by friction due to excessive unbalanced pressure upon the top of the valve, and numerous efforts have been made to overcome this objection, but with only partial success, in many instances other objections being introduced in the attempt to overcome the above-mentioned objection such as increased complication, liability to leakage, and radical change of forni-rendering the valve inapplicable to engines already constructed.

The objections above mentioned are particu larly disadvantageous in locomotive engines, which are designed with special reference to the characteristic features of the slide-valve, on account of the necessarily complicated valvegear and the frequent shifting of the same.

It is the object of my invention to produce a slide-valve which will be free from excessive unbalanced pressure, which will 'not he coinplicated in construction or liable to leakage, and which may be readily substituted for the common slide'valve without material change to the other parts of the engine, and which may be applied to any slide-valve engine already constructed.

The above-mentioned objects I attain by the means illustrated in the accompanying drawings, in Which- Figure 1 represents a perspective view of the valve-seat and valve complete; Fig. 2, a perspective view of the valve; Fig. 3, a top view of the valve-frame and valve-rod; Fig. 4, a side elevation of the valve-frame; Fig. 5, a bottom view of the valve-frame; Fig. 6, a vertical cross-sectional view of the valve entire with the valve-cover detached; Fig. 7, a lougitudinal vertical sectional view of the valve, valve-seat, and valve-cover, showing the valve in one position over the ports; and Fig. 8, a

similar view showing the valve in another position over the port-s. Figs. 9 and 10 are views of the valve-cover and valveseat. Fig. 11 is asection through valve-fraine.

In the drawings, the letter A indicates the valveseat, and B B the ports. I

0 indicates the valve-frame, which is rectangular in shape, and which is provided with right-angled lugs D,or other suitable means of attachmcntforthevalve-rod. Theframeisopen from the top to the bottom, and is arranged to slide upon the valve-seat in the usual manner. The said frame is braced by a longitudinal bar, E, which may be cast with the frame, or separately formed and secured there n, and on the outside near each end is provided with communicating grooves F at each side and on the top. In these grooves are fitted the metal packing-bars G, which are jointed together at the angles H, the thickness of the bars being less than the depth of the grooves, in order to leave a space between the bars and the bottom of the grooves, for the purpose more fully hereinafter specified. In the same vertical plane with the grooves there is a recess, N. in the under side of the valve frame, near each end.

The valve-frame is bored horizontally and vertically, forming seats for the spiral springs I, whereby communication is established between the recesses and the inter-valve spaces for the passage of steam, for the purpose here inafter set forth.

The letter L indicates the valve-cover, which is made to fit closely over the'valve, being open at the bottom and ends, as shown in Fig. 9, and is provided with dowel-pins at its lower edge, adapted to fit into recesses in the valve-seat,or othersuitable means to preventdisplacement.

The upper and side edges of the ends of the valve-frame are beveled, as indicated by the letter M, as shown in Fig. 2, for the purposes hereinafter specified.

The operation of my improved valve is as follows: The valve being at the end ofits travel, as shown in Fig. 7 of the drawings, the steamport 1 is open, admitting a full flow of steam into the forward end of the cylinder, and free exhaust from the back end. While the valve is in this position the recesses are exhausted, and consequently there is no outward pressure against the packing-bars, except that exerted by the coiled springs, which is just sufficient der side, and there results an unbalanced pressure downward to the end of the stroke.

During the movement of the valve the outward pressure upon the packing-bars is subject to the following variation: Beginning at the end of the back-stroke, as before, communication isestablished between the recess and the exhaust, as shown in Fig. 7, and consequently there is no pressure upon the bars. When the said recess passes over the bridge a sufficient distance to establish communication with the steam-port, steam is admitted, and, passing through the apertures, fills the space within the grooves, and there results an outward pressure upon the bars corresponding to the cylinderpressure. This pressure continues until the said part passes beyond the bridge, and communication is established between the steam-port I and the exhaust-port, as shown in Fig. 8, when it is exhausted simultaneously with that end of the cylinder, and remains in an exhausted condition to the end of stroke. The inner part, P, Fig. 11, of each end is also subject to an upward pressure at each alternate passage over the steam-port. The upward pressure upon this portion begins with its entrance upon the exhaust side of the steamport, and ends when that end of the cylinder is exhausted. The valve is proportioned so that the under surface area of this portion is somewhat less than the upper surface area of the beveled portion.

As'before mentioned, the interior space, E, extends from the top to the bottom, and therefore the upward pressure of the exhaust-steam does not affect the valve, this upward pressure being sustained by the cover, which in turn is firmly held down upon the seat by the steampressure upon its top.

It will be seen from the above that while the valve is subject to a variable pressure at different parts of its travel there is no position where the upward pressure exceeds'the downward pressure, and consequently the valve has no tendency to jump or rise from its seat,

thereby causing a leakage of steam.

I am aware that covered slide-valves are old; but as heretofore constructed they have been found objectionable, mainly on account of their liability to leakage in consequence of being subject at times to an unbalanced upward pressure.

Having thus described my invention, what I claim, and desire to secure by Letters Patent, 1s

The combination, with the reciprocating valve 0, havinga central steam-space, E, and grooves F, with connecting steam-passages, of the jointed packing'bars G, located in the grooves, the springs I, located in vertical and horizontal recesses, the valve-rod and its connections, and the cover L, all arranged to operate substantially in the manner specified.

In testimony whereof Iafiix my signature in presence of two witnesses.

\VILLIAM A. DOBSON.

Witnesses:

H. R. BENSON, WILLIAM MoRRIs- 

